Power line communications (PLC) include systems for communicating data over the same medium (i.e., a wire or conductor) that is also used to transmit electric power to residences, buildings, and other premises. Once deployed, PLC systems may enable a wide array of applications, including, for example, automatic meter reading and load control (i.e., utility-type applications), automotive uses (e.g., charging electric cars), home automation (e.g., controlling appliances, lights, etc.), and/or computer networking (e.g., Internet access), to name only a few.
FIG. 1 shows the structure of a physical layer (PHY) data frame 100 for an orthogonal frequency-division multiplex (OFDM) PHY based on the IEEE P1901.2 standard, including the various fields in the MAC header 130 shown. Data frame 100 includes a preamble 110, a PHY header shown as frame control header (FCH) 120, a media access control (MAC) header 130, a MAC (data) payload 140, and a Frame Check Sequence (FCS) 150.
MAC header 130 includes segment control 131, frame control 132, Seq. No. 133, destination PAN 134, destination address 135, source PAN 136, source address 137, and auxiliary security header 138. The preamble 110 and FCH 120 are indicated as being ROBO mode (Robust OFDM mode) based on ROBO modulation as used in IEEE P1901.2. ROBO modulation is robust in the sense that it may provide four times extra redundancy parity bits by using a repetition code and therefore the network may more reliably deliver data under severe channel conditions. More generally for PLC network communications, the preamble and header of the PHY frame are both generally sent in the most robust modulation scheme available, typically being in a more robust modulation as compared to the modulation used in the other frame portions, including the MAC payload 140.
The IEEE P1901.2 specification states the following with respect to the transmission of the negative acknowledgment (NACK) frame “The receiver will send NACK to the originator if it is requested and the received MAC frame is corrupted and cannot be recovered by PHY”. It is possible that the MAC header (specifically the destination address 135) in the data frame 100 may be corrupted and thus a node in the network that is not the intended receiver may receive the data frame despite not being intended to be the receiver, and thus become the node transmitting the NACK. The IEEE P1901.2 specification also has no mechanism to distinguish between MAC header corruption and MAC payload corruption.